Crossbar system switchboard construction



Feb. 3, 1953 E. L. EARLE ETAL 2,627,554

i m if INVENTORS= EDWIN 1.. EARLE m1 hm Ebm 0 5 6 m mwUm IU NON E LEARLE ETAL CROSSBAR SYSTEM SWITCHBOARD CONSTRUCTION Feb. 3, 1953 FiledOct. 25, 1949 Feb. 3, 1953 E. 1.. EARLE ETAL 2,627,554

CROSSBAR SYSTEM SWITCHBOARD CONSTRUCTION Filed Oct. 25, 1949 llSheets-Sheet 4 WORK BENCH F114 PART 2 INVENTORS EDWIN L. EARLE RICHARDP. ARTHUR MMQ-M H ATTORNEY Feb. 3, 1953 E. L. EARLE ET AL 2,627,554

CROSSBAR SYSTEM SWITCHBOARD CONSTRUCTION INVENTORS= EDWIN L. EARLERICHARD P. ARTHUR M Mia m7 ATTORNEY CROSSBAR SYSTEM SWITCHBOARDCONSTRUCTION Feb. 3,, 1953 E. L. EARLE ETAL 2,627,554 1 i Filed Oct. 25,1949 11 Sheets-Sheet 7 FIG.

LLD

INVENTORS= EDWIN L. EARLE RICHARD P. ARTHUR BYM ATTORNEY Feb. 3, 1953 E.L. EARLE ET AL 2,627,554

CROSSBAR SYSTEM SWITCHBOARD CONSTRUCTION A Filed 001;. 25, 1949 llSheets-Sheet 8 Feb. 3, 1953 E. L. EARL! ETAL CROSSBAR SYSTEM SWITCHBOARDCONSTRUCTION 11 Sheets-Sheet 10 Filed Oct. 25, 1949 Ill Ill

IIH

|NVENTORS= EDWIN L. EARLE RICHARD P. ARTHUR BM ATTORNEY Feb. 3, 1953 E.L. EARLE ET AL CROSSBAR SYSTEM SWITCHBOARD CONSTRUCTION ll Sheets-Sheet11 Filed Oct. 25, 1949 S R .m E W U TLT N R R R mmA o v P V W m L D A mmH Mm ER m w L Patented Feb. 3, 1953 CROSSBAR SYSTEM SWITCHBOARDCONSTRUCTION Edwin L. Earle and Richard P. Arthur, Chicago, Ill.,assignors, by mesne assignments, to Kellogg Switchboard and SupplyCompany, a corporation of Delaware Application October 25, 1949,Serial'No. 123,431

Claims. 1

This invention relates to a crossbar-system switchboard construction,but is not necessarily limited thereto. Its primary object is to providea switchboard of new and improved construction on which the apparatusunits required in a crossbar-switching system may be economically andefficiently mounted in a switchroom of a relatively small floor area andof a relatively low ceiling height.

A further object is to enhance the handling. of the switchboardapparatus in transit to the site of installation. This object isattained by (1) providing a switchboard of the foregoing character whichcomprises separate frame uprights so constructed that they can bemanufactured, fully wired, and shipped to the site of installationbefore the pertaining apparatus units are mounted thereon, and (2) byproviding fully wired apparatus units which can be packed and shipped tothe site of installation separately from the frame uprights and can bereadily mounted thereon. and connected to the frame wiring. Theseprovisions operate to substantially lessen the weight of the items to beshipped and handled.

Additional objects are (1) to provide frame uprights of the foregoingcharacter which, whether used singly or in groups to form a switchingframe, may have suitable fully enclosing members attached thereto whichinclude panels that. are readily removable to give access to theapparatus units thereon, and (2) to provide standardized cable-runwayparts to support the cables required to interconnect the several framesof the switchboard.

One feature of the invention is that the apparatus units are, for themost part, so mounted within the concerned frame uprights as to slide inand out in the manner of drawers. This arrangement permits efficient useto be made of frames which are relatively deep and which therefore arenot required to be of great height to accommodate a desired amount ofapparatus.

Further features are that (1) each drawermounted apparatus unit isprovided with a flexible terminal cable connecting it to the framewiring, permitting the unit to be slid out for inspection withoutdisturbing its association with the frame wiring, and (2) each terminalcable connects to the frame wiring through readily attachable anddetachable connecting members, permitting easy installation and removalof any such apparatus unit.

Other features are that (1) each frame uprights includes a built-inlocal cable runway at the top thereof, formed by cable slats attached atwith the service compartment and the individual drawer. spaces.

Other objects and features will appear as the description progresses.

I. GENERAL DESCRIPTION It has been chosen to illustrate the invention asapplied to a switchboard serving a primarysecondary-spread crossbartelephone system specifically as disclosed in the application of Bellamyand Bowser Serial No. 85292, filed April 4, 1949.

IA. THE DRAWINGS The accompanying drawings comprising Figs. 1 to 21 showviews of the chosen preferred embodiment of the invention as follows:

Fig. 1 is a general view of the switchboard, together with theassociated powerboard PB and main distributing frame MDF;

Figs. 2 and 3 show the disposition of apparatus units within the drawerspaces in any line-link frame and in the block-link frame;

Fig. 4 is a plan view of a switchroom containing the apparatus of Fig.1, with the covers removed from the cable runways which are shown empty;

Fig. 5 is a view similar to Fig. 4, but showing the runway cables inplace;

Figs. 6, 6A, and 6B are respectively a front view, a plan view, and aright-end view of a fully equipped line-link frame;

Fig. 7 is a general view of a line-linkframe only partially equipped,showing the basic construction;

Fig. 8 is a general sectional view of the ap largement of the lower-leftcorner of Fig. 9 to show the construction of panel-retaining pins I03;

Fig. 12 is a general rear view of a cover panel H;

Fig. 13 shows a typical frame cable;

Fig. 14 is a sectional plan view of the primary bay of a line-link takenalong line I4I4 of Fig. 6, to show a typical flexible terminal cable;

Fig. 15 is an enlarged view taken along line I5-I5 of Fig. 14.;

Figs. 16 and 17 show constructional details of runway bridges usedbetween frames;

Figs. 18 and 18A are respectively, a general rear view and an end viewof a double-height drawer unit composed of relay equipment andterminal-pin blocks;

Fig. 19 is a perspective view of a single-height drawer of relayequipment;

Fig. 20 is an enlarged general view of a portion of the block-link frameof Fig. 1, but with parts of the enclosing panels broken away to showapparatus underneath; and

Fig. 21 is a fragmentary sectional view taken generally along line 2I2Iof Fig. 20.

113. GENERAL ARRANGEMENT (FIG. 1)

"Referring generally to the drawings, and particularly to Fig. 1, theillustrated crossbarsystem switchboard contains the switchboardapparatus required in the primary-secondaryspread crossbar telephonesystem, comprising a 1000-line telephone exchange, disclosed in thenoted Bellamy and Bowser application. Such an exchange serves a maximumof one thousand local subscriber lines, and has porvisions for fortyincoming and forty outgoing tie trunks connecting with other points.

The main distributing frame MDF of Figs. 1, 4, and 5 is of well-knownconstruction. The conductor pairs representing the subscriber lines andthe noted tie trunks terminate on one side thereof, while the conductorpairs representing switchboard terminals terminate on the other side,and the terminals on the two sides are interconnected by two-wirejumpers as indicated in the noted prior application.

The apparatus for supplying the required direct-current andalternating-current power to the switchboard frames, and for supervisingit, is

mounted on powerboard PB, which may be of any desired construction, butpreferably matches the switchboard apparatus in height and appearance,as shown.

Frame TC is the trunk-coupler frame of the noted application, havingmounted thereon the trunk couplers required to be used in connectionwith the above-noted tie trunks.

Frames LLA to LLD are line-link frames A to D of the noted application,each terminating 250 subscriber lines. Frame BL, seen in the foregroundin Fig. l, is the block-link frame of the noted application. It iscommon to trunk-coupler frame TC and line-link frames LLA to LLD, as allcalls handled by the switchboard pass therethrough.

The switchboard frames are preferably of a uniform height and depth.Each frame has such width (or runninglength) as is required according tothe amount of apparatus to be mounted thereon. Each frame comprises oneor more frame uprights having the type of construction shown in Fig. 7for line-link frame LLD.

Each frame is surmounted by a local cable runway extendinglongitudinally thereof (parts 23,

4 25, and 35 for frame LLD, Fig. '7). These runways are covered bysheet-metal covers I4 to I8, Fig. 1. .The local runways areinterconnected with each other and with powerboard PB by covered runwaybridges 3 to I2 of Fig. 1.

Runway sections I and 2 interconnect main distributing frame MDF withframe LLA and frame TC respectively. These runway sections are leftuncovered to match the open construction of frame MDF, whereat thenecessity for making relatively frequent and extensive jumper changesrenders the use of enclosing members undesirable.

The enclosing members for frames TC, LLA to LLD, and BL include elevenhorizontal removable panels I15 front and rear for each frame or baythereof. The eleven spaces respectively covered by these panels comprisea service compartment indicated at SC in Figs. 2, 3, 6, and 6B, followedby ten drawer spaces numbered I to II! as indicated in Figs. 2 and 3.The service compartment S0 at any frame is the space between the cablerunway thereof and the baflie I5 thereof (Figs. 6, 6A, 6B, and 7), whichact as protective covers for the underlying drawer spaces.

10. DRAWERSPAGE ASSIGNMENT (FIGS. 2 AND 3) Referring to Figs. 2 and 3,the assignment of apparatus units to locations in the ten drawer spacesof the switchboard frames will be described.

ICl. Line-link frames (Fig. 2)

The identity of the apparatus units mounted in the drawer spaces (I toID) of any line-link frame LLA to LLD is given in tabulated form in Fig.2. Any such frame comprises a primary bay PB and a secondary bay SB. Theuppermost compartment in either bay is the service compartment SC.

Ten primary crossbar switches occupy drawer spaces I to II] respectivelyof the primary bay PB of any such frame. They are the line-link primaryswitches 800 of the Bellamy and Bowser application.

Five secondary switches occupy the drawer spaces I to 5 of the secondarybay SB. They are the line-link secondary switches 900 of the lastnotedapplication.

Drawer spaces 6 and I of any bay SB are occupied respectively byline-controller switches I and 2. They are the line-controller switches1000 and 1100 of the last-noted application.

Drawer space 3 of bay SB is occupied by a line controller, which isline-controller 1200 in the last-noted application.

Drawer spaces 9 and III of any secondary bay SB are vacant.

As pointed out in the Bellamy and Bowser application, each of thecrossbar switches used in the system is preferably of the type disclosedin the pending application of R. P. Arthur for a Crossbar Switch, SerialNo. 8,900, filed February 17, 1948. Each such switch has an overallappearance about as shown at PI, SI, and P5 of Figs. 6 and 6B, and eachhas a pair of rollers 51 (see Fig. 8) at each end thereof to facilitateits desired sliding operation as a drawer.

All control relay apparatus used on the disclosed switchboard ispreferably of the type disclosed in the pending application of Bellamyand Arthur for Electromagnetic Relays, Serial No. 20,196, filed April10, 1948. The noted line controllers (drawer space 8 in any secondarybay SB) each employ the noted relay apparatus mounted to comprise arelay drawer as shown at RD in Fig. 19.

1C2. Block-link frame Referring now to Fig. 3, the disposition ofequipment on the block-link frame BL shown therein will now bedescribed.

Block-link frame BL is composed of seven bays, secondary bay .BL-S,control bay BLC, and primary bays BLP| to BL-P5. The uppermostcompartment in each bay of the block-link frame is the servicecompartment SC, as explained for the line-link frames.

102a. SECONDARY BAY In secondary bay BL-S, the ten drawer spacesunderneath the service compartment are occupied by secondary switches ito ID, each of which is a crossbar switch of the construction previouslyreferred to. They are the block-link secondary switches 1400 of thenoted Bellamy and Bowser application.

IC2b. CONTROL BAY Referring to control bay BL-C, Fig. 3 shows that thefirst two drawer spaces are vacant, while the third drawer space isoccupied by miscellaneous relay appartus (Misc) This apparatus ismounted on a relay drawer such as RD of Fig. 19, relay apparatus thereoncomprises section preference relays 1550 and the outgoing :5

controller 1700 of the identified Bellamy and Bowser application.

Drawer space 4 is occupied by a crossbar switch serving as theblock-controller switch 1500 of the Bellamy and Bowser application.

Drawer spaces 5 and 6 of the control bay are occupied respectively byduplicate block controlle'rs (B. C. l and B. C. 2') each of whichcomprises a drawer of relay equipment such as is shown at RD in Fig. 19,and wired as shown for the block controller 1600 of the Bellamy andBowser application.

Drawer spaces 1 and. 8 of the control bay are occupied by equipmentwhich is shown in circuit diagram in Figs. 18 and 19 of the Bellamy andBowser application and identified as block translator 1800. Physically,this unit of equipment comprises apparatus mounted on the double heightdrawer shown herein in Figs. 18 and 18A. The apparatus mounted on thefront portion of the drawer comprises the relay apparatus of Fig. 18 ofthe Bellamy and Bowser application, while the apparatus mounted on therear (at 131) comprises the terminal-pin blocks shown in Fig. 19 of theBellamy and Bowser application.

Drawer spaces 9 and H) of the control bay BL- C are vacant, as noted fordrawer spaces 1 and 2 thereon.

1620. PRIMARY BAYS Referring now to the five primary bays, B'LPl toBL-P5 of the block-link frame BL, each has two sections of blockcouplers mounted thereon in drawer spaces I to 8 as shown in Figs. 20and 21 for the final primary bay BLP 5. There is a section of twentyblock couplers I mounted on the rear of each bay as shown in Fig. 20,and a similar section of twenty block couplers 150 mounted on the frontof the bay as indicated in Fig. 21. Each block coupler includes aseparate angularly shaped common magnetic return plate, together withrelay apparatus mounted thereon, together with countingapparatuspreferably of the general type disclosed in the application of Bella-myand Arthur for Electromagnetic Counting Devices, Serial No. 43,436,filed August '7, 1948. Any such block coupler has its relay and countingapparatus interconnected for operation as disclosed, for example, inFig. 5 of the Bellamy and Bowser application.

'I en primary switches (PRI. SWI to PR1. SWIG) are mounted in pairs indrawer spaces 9 and ID of the five primary bays BLPI to BL--P5. Theseare the block-link primary switches 1300 of the Bellamy and Bowserapplication. The section of block couplers mounted on the front of anyprimary bay is associated with the primary switch in drawer space 9,while the section of block couplers mounted on the rear of the bay isassociated with the primary switch in drawer space H] of the same bay.

ID. SERVICE COMPARTM-aNT EQUIPMENT (FIG. 4)

Fig. 4 shows the floor plan of a switch. room containing the switchboardapparatus of Fig. 1 and associated powerboard and distributing frame,together with battery 20! for supplying direct current to theswitchboard apparatus, charger 202 for charging the battery, and thecustomary workbench 203. The switchboard apparatus is illustrated inFig. 4 as it appear with covers removed from the cable runways, and withthe runway cables uninstalled to permit an unobstructed view ofequipment in the service compartment of the switchboard frames.

In any line-link frame LLA to LLD, a fuse panel 82 is located in theservice compartment of the secondary bay, as seen most clearly in Figs.6, 6A, and 6B. Items BI and 83 are similar fuse panel-s located in theservice compartment of trunk-coupler frame TC, and secondary bay BLS ofthe block-link frame BL, respectively.

Items 19 and B0 in Fig. 4 are terminal-pin blocks located in the servicecompartment of the primary and secondary bays respectively of any one ofthe line-link frames LLA to LLD, a seen most clearly in Figs. 6, 6A, and6B. Items ll 53 in each of the primary bays BL-Pl to BIL-P5, togetherwith the two items I54 in control bay BL-C and item I55 in secondary bayBL-S, are similar terminal-pin blocks located in the service compartmentof the bays of block-link frame BL.

When the usual connections (not shown) have been made and cables havebeen run as shown in Fig. 5, direct current from battery 20! is suppliedthrough powerboard PB tothe noted fuse panels located in the respectiveframes, and through separate fuses on the fuse panel of any such frameis supplied to respective apparatus units thereon.

Generally speaking, the control wires and talking-path wires whichrequire to be connected externally at any switchboard frame are carriedthrough frame cables to terminal pins in the associated one of the notedterminal-pin blocks 19, 80, and I53 to I55. Desired ones of theterminals in these pin blocks are interconnected with terminals on oneor another of the switchboard frames, on the distributing frame MDF, oron powerboard PB, by cables installed in the cable runways as shown inFig. 5.

IE. RUNWAY Cinemas (FIG. 5)

Referring now to Fig. 5, the runway cables comprise groups '30! to 306as follows:

The cables in group 353i extend from powerboard PB to. each of theswitchboard frames 'IC, LLA to LLD, and BL, carrying the necessarydirect-current and alternating-current and signal or supervisory wiresto any such frame;

The cables in group 3E2 carry the conductor pairs between frames TC andMDF required for the noted two-conductor incoming and outgoing tietrunks;

The cables in group 303 extend between frame MDF and line-link framesLLA to LLD to .carry the two-conductor subscriber lines betweenthframes;

The cables in group 3% contain the three-wire outgoing-trunk branchesand the three-wire incoming-trunk branches between trunk-coupler frameTC and block-link frame BL;

The cables in any one of four groups 305 carry the originating andterminating trunks, along with associated control conductors between theconcerned line-link frame LLA to LLD and the block-link frame BL; and

The cables in group 383 interconnect the control bay BL-C of the blocklink frame with the block-link primary switches mounted on primary baysBLPi to Elli-P5.

For the most part, the Wires in the foregoing cables connect toindividual terminal pins in the pin blocks l9, Bi! and IE3 to I55 shownin Fig. i but omitted in Fig. 5 to avoid crowding and confusion.

II. DETAILED DESCRIPTION llA. FRAME CONSTRUCTION (Fins. 6 AND 7)Referring particularly to Figs. 6, 6A, 6B, and

7, the construction of line-link framde LLD of Figs. 1.3, i, and5 willbe given, keeping in mind that frames LLA to LLD are all like inconstruction.

As seen best in Fig. 7, frame LLD includes three principal front members2 l 22, and 23, and

three oppositely disposed principal rear members 24, 25, and 26.Considering the noted principal front members. 2! and 22 are uprightchannel bars on which member 23, a horizontal angle bar, is laid andwelded to the ends thereof, providing a rigid inverted U-shapedconfiguration.

Rear members 24 to 26 are similarly welded together to form a mirrorimage of the welded front member.

The noted front and rear U-shaped assemblies are placed in the relativelocations shown in Fig. 7 and are welded to end floor plates 35 whichhold the bottom of the assemblies at the desired distance from eachother. Cable slats 36 are welded to the horizontal webs of top anglemembers 23 and 25 to hold the top of the assemblies at the desireddistance from each other. Parts 3 and 36 combine the front and rearassemblies into a comparatively rigid frame.

Frame LLD is divided into the two bays, primary bay PB and secondary baySB, by the intermediate upright channel members 21 and 28, which arewelded to intermediate floor plate 35 and to the underside of horizontaltop members 23 and 26.

The E-shaped frame structure thus far described is brought intoconstructional four- 1 sided shape by the addition of the centrallydisposed longitudinal channel member 33, which is welded to cross angles29 and 39, welded in turn to the left-end and right-end uprightchannels, respectively- Channel 33 is further welded to members (such as21, 28) as needed. That is,

trunk-coupler frame TC is a single-bay frame upright; the startingsection of block-link frame BL is a two-bay frame upright similar to anylinelink frame; and each of the primary bays BL-Pl to BLP5 is asingle-bay frame upright.

The several frame uprights comprising frame BL are preferably boltedtogether, as by bolts passing through holes (not shown) in adjacentupright end members, similar to end channels 2 l, 22, 24, 25 of Fig. 7.This sectionalized construction of frame BL promotes handling andshipping, as well as permitting unneeded primarybay sections to beomitted as in small initial installations.

IIB. SLIDE Sorrows Ten pairs of slide supports 40, for drawer slides 50(Fig. 8) are secured to the defining uprights (2|, 2%, 21, 28) ofprimary bay PB and ten similar pairs of slide supports 39 are installedin secondary bay SB, on its defining uprights, (21, 28, 22, 25 Slidesupports #6 are secured to the upright members by screws 43 as shownbest in Fig. 8. When installed, these slide supports add to thepreviously noted rigidity of the frame structure.

Any one of the first nine drawer spaces discussed hereinbefore is thespace between the top 7 of the concerned pair of slide supports 40 andthe top of the next underlying pair of slide supports, while the tenthdrawer space extends from the top of the lowermost pair of slidesupports to the top of angle members such as 29 and 31.

11-0. RAFFLE PLATES A sheet-metal baffle plate 15, having its front andrear edges turned up for rigidity, is laid on the two uppermost slidesupports 40 in the primary bay PB, as a protective cover for theequipment units mounted in the underlying drawer spaces, and a similarbaiiie plate 25 is provided for the secondary bay SB. Baffle plates 15may be secured in place by screws entering tapped openings 44 providedin each slid support 46, as seen best in Fig. 8.

Bafrle plates 15 define the lower limit of the service compartmentindicated at SC in Figs. 6 and 6B.

IID. DBAXVER MoUN'rmcs As previously pointed out, each equipment unit isfitted into its assigned drawer space within the concerned switchboardframe so as to move in and out as a drawer. Most of the drawermountedequipment units are crossbar switches, and each is equipped with a pairof studsupported rollers at each end. These rollers and studs are shownat 10 and 11 of Figs. 1 and 2 of the previously noted application ofArthur.

In Fig. 8 and in Fig. 10, the two rollers at one end (the left) of theeighth and tenth crossbar switches, respectively, of primary bay PB offrame LLD (Fig. 7) are shown at 57. Their supporting studs 58 are shownin section, as the noted switches are omitted from the drawings topermit an unobstructed view of the slide mechanism.

At any slide mechanism, rollers 51 are resting within a roller channelformed indrawer slide Si! by turning the lower portion thereof inwardasets;

'9 ly and turning the edge portion upwardly as shown at Fig. 8.

In Fig. 10, the rollers 51 and slide 50 are shown in the position theyoccupy when the associated apparatus unit is entirely within the frame,

while in Fig. 8, drawer slide 50 and rollers 51 are shown in theposition they occupy when the concerned apparatus unit has been pulledpart way out. Incident to this operation, each outward roller 5': hasengaged outward stop 55 (a bentover tongue attached to slide '50), andhas pulled drawer slide 50 outwardly to the illustrated position. Thismovement of part 55 occurs within the slide-support channel formedwithin the lower portion of member 40 by a latoral and an upward formingoperation to provide guide portion 42.

As seen best in Fig. 8, tipping of slide 50 within slide support 48 islimited by the shank and enlarged head of stud 45, rigidly secured tomember 40 as by having a reduced portion of the stud passed through ahole 46 (see next underlying slide 45, Fig-8) and riveted over on theother side. In the noted guiding action, the upper surface of theinwardly shear-formed portion 52 cooperates with the shank of the stud45, while the inner edge thereof cooperates with the enlarged head ofthe stud.

Referring further to Fig. 8, when the apparatus unit in question ispulled further out, the

limit is reached when the shank of stud is encountered by the abutment54 left in part by shear-forming as noted to produce part 52. The unitthen occupies a position as shown at Pl, Fig. 6B.

When the fully withdrawn apparatus unit in question is pushed inwardlyinto place within the confines of the switchboard frame, its rollers 51first rotate about studs 58 to allow the unit to roll inwardly aconsiderable distance before the isfirst completely assembled, bytelescoping parts 44 and 50 together and then riveting stud in place,following which the assembled slide mechanisms are secured in place byscrews 45,

inreadiness for the roller-equipped apparatus units to be installed. Itshould be noted that parts 45 and 51! are omitted from parts 49 in Fig.7, and in one instance in Fig. 8, merely for clarity of illustration andto avoid crowding the drawing, ratherthan to indicate that parts 45 and'59 are applied after parts 40 are secured to the framework.

Keeping in mind that each drawer space is equipped with two slidemechanisms (2. lefthand one as shown in Fig. 8), and a right-hand one(not shown in detail), when a roller-equipped apparatus unit is to bemounted within a drawer space the left and right slides 55 are firstpulled out until each is stopped by contact between the associated stud45 and surface 54. Then, the inward left and right rollers 510i theapparatus unit are introduced into the portion of their slides 5!} whichlies outwardly from guide portion 52, as by tiltin downwardly the inwardportion of the otherwise horizontally held unit. The unit is then movedpartially into its drawer space to pulled out to the position shown atPI, Fig. 6B,

it may be inspected from above and below. If further access is desired,it may then be tilted upwardly to disengage its outward rollers 51 (Fig.8) from their slides 59, following which the entire unit may be pulledforwardly until the inward rollers 57 thereof are stopped by outwardstops 55. The apparatus unit may then be held firmly and rotatedupwardly about its inward rollers until the under side of the unit isexposed to hori zontal View, or it may be rotated downwardly to bring"its top side into horizontal view when it reaches the pendant positionshown at P5 in Fig. 6B. The pulled-out and partially detachedap paratusunit may thus be rotated more than 180 degrees about the horizontal axisdefined by its inward rollers. This may be done quite readily even witha comparatively heavy apparatus unit, as the weight of the unit, or alarge part of it is borne by the inward rollers, which are left attachedto their respective slide mechanisms. Keeping in mind that the slides51] are in fully pulled-out position when the noted rotation of theapparatus unit occurs, the net external force applied to the apparatusunit should be outwardly, against outward stops 55, to avoid undesireddrawer action.

Following its noted partial detachment from the slide mechanisms, theapparatus unit may be returned to its normal fully attached position bya reversal of the described partial detaching operations.

HE. FRAME WIRING Each switchboard frame (each frame upright in the caseof sectionalized frame BL) contains frame wiring suitably related to thewiring represented by the described runway cables, groups 30| to 306,Fig. 5. In describing the frame wiring, line-link frame LLD of Figs. 1,2, and 4 to 7 has been selected as typical, and the frame wiringrequired in the primary bay PB of this frame to connect the concernedsubscriber lines to the ten primary switches thereof has been selectedas a typical example. This latter frame wiring is contained in cable 50,Fig. 13, shown detached from the switchboard for clarity ofillustration. Cable 95 extends from line-terminal blocks 79 in theservice compartment of the primary bay to the respective drawer spacesof the primary bay, having a separate horizontal leg 92 for each drawerspace.

When cable is installed, the vertically disposed portion thereof lies inthe space between the upright left-end members 2! and 24 of frame LLD asshown in section in Fig. 14. The main horizontal portion iii of cable 9ilies within the service compartment SC (Fig. 6) of the frame, where theindividual wires are connected to respective terminal pins in blocks 79.

Cable 90 and legs 92 thereof also may contain local wires extendingbetween drawer spaces as desired. Frame cables interconnecting the unitsof bay PB with units of bay SB may have the vertically disposed portionsthereof located in the space between intermediate vertical members 2'!11 and 28 (as shown at 96a, Fig. 14), still further cables (not shown)may be located in the space between right-end vertical members 22 and 25to serve the apparatus units of secondary bay SB of the frame.

lIF. CONNECTING STRIPS AND TERMINAL GABLES Pursuant to (1) permittingthe frames to be fully wired separate from the apparatus units, (2)permitting the fully wired units to be readily installed, and (3)permitting the installed drawer-mounted units to be withdrawn andreturned as described while remaining operationally connected to theframe wiring, the individual wires (such as 93, Fig. 13) in any drawerleg such as 92 of cable 93 are connected to individual terminals (-31 ina pair of aligned terminal strips 6t, and each drawer-mounted apparatusunit is provided with a flexible terminal cable ending in one or moresimilar terminal strips having terminals which register respectivelywith the terminals in the first-noted strips when the strips are placedtogether.

The noted terminal strips are preferably compression-connecting stripsof the type fully disclosed in the application of Earle et al. forCompression-Connecting Terminal Apparatus, filed December 20, 1948.

The compression-connecting terminal apparatus for any drawer space iscarried on horizontal angle bars 60 of Figs. '7, 14, and 15. Those forany drawer space i to 9 in a bay are mounted on brackets 62 secured tothe upper surface of slide supports 4% of the next underlying drawerspace, while those of the tenth drawer space are mounted on brackets 13and 62 (Fig. secured to the underlying angle bars 29 to 32.

While Fig. 7 shows support bars 6!! installed for only one drawer space(#4 in bay SB), it will be understood that each drawer space in each bayof the frame (excepting the two labelled vacant in Fig. 2) is equippedwith a set of bars Ell. Each bar 66 has a number of studs 6! disposedtherealong to locate and clamp the terminal srips to be placed thereon.Referring to Fig. 10, two support angles 85], extending across the lowerportion of the tenth drawer space of bay PB, Fig. 7, are welded at theirleft end to the two arms of bracket 62, and are similarly secured at theother end (not shown). Bracket 62 is secured to the upper face ofadapting bracket i3, secured to the lower web of angle bar 29 by screwsM.

As shown in Figs. ll) and 15, the bracket 62 at either end angle bars 69for any any drawer space I to 9 of bay PB (Fig. 7) is secured by a screw63 to the upper flange ll of the next underlying slide support 40.

As shown best in Fig. 15, the compression-connecting terminal assemblyfor any angle bar 56 is applied to the rear sloping surface thereof, theone to Which studs 6! (Figs. 7, 10, 15) are attached, as by spotwelding.

Thin insulator strip 3 is first applied to *bar 60, studs 6| beingreceived by location holes (not shown) in strip 64. Spacing insulatorstrip 65 is next applied, followed by a terminal strip 66 (see Fig. 13)to the terminals 57 of which respective wires 93 of the concerned leg 92of cable 90 have been secured. The cable leg 92 is convenientlysheltered within the confines of the associated angle bar til. The notedparts 64, 65, 66, and 6! correspond respectively to parts 5, 2, 4, and16 of Figs. 1 to 10, in the noted application of Earle et a1.

During manufacture and assembly of the switchboard frame underdiscussion, the noted assembly of the wired terminal strips 66 onsupport bars 68 is followed by the assembly of insulating strips H1,bars fl, and clamp nuts 12, which are tightened for shipment. The partsmay remain so assembled until the frame wiring has been tested; theframe has been shipped and installed; the switchboard frames have beenconnected together by the described runway cables; and thedrawer-mounted apparatus units have been installed and are ready forconnection to the frame wiring.

As shown in Figs. 6, 6B, 14, and 15, each drawer-mounted apparatus unitis provided with a terminal cable 34 having flexible forward branches 85connected to the unit, and having fixed rearward branches 86 whichafford connecticns to the frame wiring. When such a unit is undergoingthe manufacturing operations, the wires in branches 85 of its terminalcable are connected to respective terminal members (not shown) of theapparatus unit, and the wires in fixed branches 86 of the cable areconnected to respective terminal members 69 contained in terminal strips8 (Fig. 15), which are reversed in position to adapt them tocooperatively overlay the respective strips 66 at which the frame wiringhas been terminated.

When the terminal wiring of an installed drawer-mounted apparatus unitis to be connected to the frame wiring, the nuts 12, clamp strips H, andouter insulator strips H1 (Fig. 15) are removed from the concernedterminal-assembly groups, following which the terminal strips 68 towhich the terminal-cable wires 81 have been attached are laid uponrespective frame strips in the relative positions shown in Fig. 15.Parts I0 and H are reapplied to studs 61 and nuts 12 are reapplied andare tightened securely. The wires 81 in the terminal cable are therebyconnected respectively to the frame wires 93 through terminals 69 and81, which are in contact with each other in overlying registry in thestrips 63 and 66 by being woven through the openings in the strips, asclearly disclosed in the noted Earle et al. application. Preferably themain part of cable 84 is fixed rigidly with the support bars 6B, as bylashing the butt ends of cable legs 86 thereto by lacing twine.

Fig. 14- shows a cable 90a lying between intermediate vertical channels21 and 28 in association with the forward support bar 69 at theindicated drawer space, while cable 90 of Fig. 16 is shown associatedwith the rearward support bar 69. The portion of the terminal assemblyassociated with cable 99a has been omitted from Fig. 15 as unnecessaryduplication of the assembly shown therein.

Referring further to Fig. 14, the apparatus unit served by theillustrated terminal cable 84 does not show because of the level (seeFig. 6) at which the view was taken. It has been found desirable tolocate each terminal cable 84 along the center of the drawer space asseen best in Fig. 14. This leads naturally to a symmetrical constructionproviding two smaller flexible legs The central location of cable 3 isrendered feasible by providing two similar terminal assemblies on eachsupport bar (in, a left assem bly and a right one as seen best in Fig. 1.1..

The outer ends of flexible legs are attached to the apparatus unit asshown at PI and P5 (Fig. 6E). Legs 35 are shown by the full lines inFig. 14 in the approximate position they occupy when the apparatus unitis in its normal position within the frames. The dotted :lines show theapproximate position to which cable legs05 flex when the unit is fullywithdrawn to the position shown at PJI, Fig. 618. Parts 85 flex therequired further amount when the apparatus unit is manipulated ashereinbefore explained to detach the outward rollers thereof and is thenpulled clear and rotated upwardly, or downwardly as at P5, Fig. 6B.

IIG. 'ENcLosrNc MEMBERS The enclosing membersemployed will now bedescribed with particular reference to line-link frame LLD, chosen astypical. The enclosing members at this frame are (1) two end panels I(Figs. 6 to 10), (2) two mullions I06 (Figs. 1, 6, and 7), (3)forty-four removable door panels H5, eleven front and eleven rear foreach of the bays PB and SB (Figs. 1, 6, and 12) and (4) four bottompanels H0 (Figs. 6, 613, 7,9, and 10). All of the noted parts bearingthe same reference character maybe identical except that the greaterwidth .of primary bay PB requires longer bottom and door panels H0 andH5 than for the corresponding parts used at'secondary 1 bay SB.

As shown in Figs. 6A, and 9, each end panel I00 is of channel-1ikeconstructionand encloses the end and a small portion of the front andrear faces of the frame. The width of amember I00 is suflicientlygreater than the depth of the frame that it may be offset inwardly toform corners ml to receive the ends of door panels H5 flush with the endpanels (Figs. 1 and 63).

End panels I00 are secured to the end'members (2|, 24; 22, 25) of frameLLD by a suitable number of oven-headed screws I02, Fig. 11. Each panelI00 is preferably cut square at the top (Figs. 1 and 7) at the level ofthe upper edge of the uppermost door panels H0, while the lower end ofeach may have the tongue-like cen tral portion shown in 6B which extendsdown sufficiently to conceal the ends of longitudinal bar 33, while thefront and rear portions of the end panels preferably terminate on thesame level as the lower line of bottom enclosures H0.

Each end panel I00 is provided with twentytwo inwardly extending pinsI03 (Fig. 11) eleven front and eleven rear for supportingcover panels H5in cooperation with notches II 9 (Fig. 12) in the cover panels. Each pinI03 has'a threaded portion of reduced diameter passing through a hole inpanel I00 and held by anut I04.

Each mullion I00 of frame LLD has a narrow finish portion flush with thecovers I I5. finish portion lies between two portions of the mullionwhich are inwardly offset to provide corners such as corners I0I in endpanels I00. 'The mullions are secured to the framework as described forend panels I00, and are similarly provided with pins such as I03, Fig.11, for supporting the inside ends of cover panels H5.

As shown in general rear view in Fig. 12, each door panel H5 has top,bottom, and side flanges H5, H1, and H0 turned up for rigidity. Theseflanges may be tack-welded at their intersection points if addedrigidity is desired. A depending flange I20, of slightly reduced widthand having the tapered corner portions indicated at I2I, extendsdownwardly from the inner edge of bottom flange H'I. When a door panelII 5 is installed, the tapered tip of its depending flange I20 is behindthe upper part of the next underlying cover panel H5. Flange I20 thuscloses the rear of the horizontal inter-panel opening The.

"114 left between adjacent door-panels to permit the hereinafterdescribed vertical sliding action rev,quired to engage and disengage thedoor panels incidental to installing and removing them.

7 Each of the two bottom panels H0 for primary bay PB, for example,closely underlies angle bars 29 and 3I (Figs. '7 and 10), and each has.an inner portion H2 of a reduced width which will pass between theangle bars 29 and 31 .tion H2 is upwardly offset to overlap the uppersurface of channel bar 33. The outward edge of Poreach panel I I 0 isturned upwardly to provide a strengthening finish flange III. Two screwsH3 (Figs. 7 and 10) pass through each flange III to hold the panel H-0to the frame members such as 2| and 24. Spacers H4, which may bebentover end tabs of flange II I, hold'the flange spaced outwardly asufiicient distance to permit the tip of the depending flange I20 of thelowermost door panel H5 to slide down behind it when the door panel isinstalled.

With the end panels I00, mullions I06, and bottom panels I I0 installedon frame LLD as described, the forty-four door panels H5 may beinstalled, eleven for the front and eleven for the rear in each bay PBand SB. During installation, any cover panel H5 is held opposite itsopening shaped notch H9 receives the associated support pin I03 (Fig.11),.carried by end panel I00 and mullion I06, permitting the coverpanel to move inwardly to the desired flush position. Then the panel H5is allowed to drop bodily to its final position wherein the toppartthereof is held against outward movement by the noted pins I 03 beingreceived in the vertical portion of notches I I9, and the bottom part ofthe panel is held against outward movement by the tip of dependingflange I20, which has slid behind the upper portion of the nextunderlying cover panel, or

A behind the upstanding flange I I I 0 (Figs. 7, 9, 10) of theassociated bottom panel I I0.

An installed cover panel H5 may be removed by lifting it to clearthepins from the vertical portion of notches H9 and to clear the'tip ofdepending flange I20 for outward movement. Thiszlifting may beaccomplished by inserting the fingers in the horizontal space betweenthe main portion of the concerned cover panel and y as a whole.

the one below it. When so lifted, the panel may be bodily movedoutwardly from the frame.

The foregoing describes the enclosing of the principal portion of thebottom of the equipment space within frame LLD, together with the endsand the front and rear faces thereof. The top of the service compartmentin the frame is left open except for the runway covers hereinafterdescribed. The top of the uppermost drawer space in each bay is closedby the previously described baflleplatesl5 (Fig. 7), which act as acover for the ten underlying drawer spaces If desired, similar ballieplates may be applied as individual covers for the respective underlyingdrawer spaces.

The three cablewells between the upright structural members of frame LLDare preferably en- .15 closed at the top and bottom to complete theenclosing of the switchboard space in which ap paratus units aremounted. These cable wells comprise the one between members 2| and 24,and the ones between members 2'! and 28, and members 22 and 25. As shownin Figs. 9 and 10, the bottom of the cable well between members 21 and25. is closed by well panel 95, sized to match the outline of the well.Two flanges 96, of a length of fit between members 2! and 22, are turneddown at the sides. Screws 9? enter these flanges to secure the wellpanel to end panel lilil and to angle bar 2%.

A similar well panel (not shown) may be used at the top of the well, ona level with the baffle plates 15 and secured between the associatedslide support it and end panel its. The top well panel, suitably slottedto accommodate cables such as 90 (Figs. 13 and 14) which may be suitablygrommeted to fill the cable-receiving notch (not shown) without chafingthe cable.

The remaining cable wells of the frame are similarly enclosed at the topand bottom.

IIH. FRAME BL From the foregoing detailed description of line-link frameLLD, which applies to any of the three similar two-bay, single-uprightframes LLA to LLD, the construction of the single-bay frames PB and TCwill be apparent. The construction of the multi-upright block-link frameBL, however, may require some additional explanation;

Frame BL comprises six frame uprights placed end to end as shown inFigs. 1, 4, and 5. The starting section of frame BL is the two-bayupright which contains secondary bay BL-S and control bay BL-C. Exceptfor the somewhat different bay widths ordinarily required, this uprightis similar to any one of the line-link frames LLA t LLD.

The noted two-bay starting section of frame BL is succeeded by fivesimilar frame uprights (or frame sections) comprising primary bays BL-Plto BL-P5, respectively. The adjacent ends of the uprights comp-risingframe BL may be bolted together as desired to maintain them inalignment, as by bolts passing through holes in the outside webs of thecorner members corresponding to parts 2I, 24, 22, 25 of Fig. 7.

The enclosing members for frame BL include end panels I90 attached tothe end uprights of the frame together with bottom enclosures, baffleplates, and cable-well enclosures as described for frame BL, and doorpanels I I5. The door panels are removably mounted on the frame by pinssupported on end panels I 00 (see Figs. 8 and 11) and on mullions I06and 106W. Mullion loll of frame BL is similar to mullion I06 of frameLLD, and mullions IUEW are similar to mullions Hi6 except that they arewider in that each covers a portion of two adjacent frame uprights,being secured to each.

IIJ. CABLE RUNWAYS As noted, each frame upright includes a local cablerunway extending along the top thereof. As seen best in Figs. 6, 6A, and'1, the local runway of frame LLD comprises the horizontal structuralbars 23 and 26, together with the slats 36 extending between them andwelded thereto. The slats 35 support the cables shown in Fig. 5, whichare preferably laced or otherwise secured to the slats 36 in the desiredgroups and layers.

bridges 3 to I2 as shown best in Fig. 4.

The described local runway of frame LLD is typical of the local runwayat the other frames, as seen best in Fig. 4.

As before explained, the runways local to the several frames areinterconnected by runway VJith inter-frame aisles of uniform width(Figs. 1, 4, 5) all of the runway bridges 3 to I2 are similar andinterchangeable.

It will be noted that each bridge 3 to I terminates at the side of eachof the two frames which it interconnects, while each bridge 3 to I2terminates at the end of the frame to which one end of it connects, andis at the side of the frame to which the other end connects. The bridges'i and I2, which connect with line-link frame LLD have been chosen toillustrate the two noted relationships, and are therefore illustrated insome detail in Figs. 16 and 1'7, respectively.

Each cable bridge I and I2 is a trough-like sheet-metal member havingits width dimension about the same as the depth dimension of theswitchboard frames. Cable slats I22 are secured to each bridge as bywelding. They correspond to slats 36 (Fig. 7) of the local runways ofthe frames, and are upwardly offset to facilitate lacing the cablesthereto.

At each end of either bridge, there is a vertical leg [25, comprising adownwardly bent extension of the bottom wall of the bridge. Leg I25 endsin a foot I26.

At frame LLC of Fig. 1 (similar to the described frame LLD) foot I26 ofbridge I (Fig. 16) rests on the bottom flange of structural angle bar26, and is secured thereto by screws I21, and the other end of thebridge (not shown in Fig. 16) terminates similarly at frame LLD.

At frame LLD (see Fig. 17) leg I 25 of bridge 12 tands between the sideflanges of structural members 23 and 26, and foot I26 rests on thebottom flanges of these members and is secured thereto by screws I21.

Each runway bridge is provided with a sheetmetal cover I23, shown brokenaway in Figs. 16 and 1'7 to expose the interior of the bridges, butshown in full in Fig. 1.

As noted hereinbefore, runway sections 5 and 2 (Fig. 1), which connectframe MDF with frames TC and LLA, are of the usual open construction.They may be secured to the frames in any desired manner, as by bolts(not shown).

As shown in Fig. 1, the local runways on the several frame are providedwith box-like sheetmetal covers I3 to I T, which have portions of theirsidewalls and endwalls removed as required for communication with runwaysections I and 2 and. covered runway bridges 3 to I2.

At the single-upright frames PB, TC, and LLA to LLD, sing1e-piece runwaycovers I3, it, and I5 are used. They are similar except for lengthvariations.

At the multi-upright frame BL, a separate section of runway cover(starting section IS, four intermediate sections H, and final sectionit) is used at each frame upright. Starting and final sections I6 and I8each have one end closed and one end open, while each intermediatesection IT has both ends open. Each section I5 and I'd may have theforward end portion expanded to telescopically receive the adjacent endportion of the next succeeding section, as is common practice insheet-metal work.

Referring again to Figs. 6 and 6B, the cover I5 for frame LLD has sideopening I9 for receiving one end of bridge I (Fig. 1) and end opening 201? to receive one end of bridge I2 (Figs. 1 and 6). The other covers andcover sections have similar bridge-receiving openings as required.

Each runway cover preferably has a sidewall configuration as shown bestin Fig. 6B for cover I5. The sidewall is offset outwardly near thebottom thereof to provide a widened portion which receives the topstructural members of the frame, while the widened portion ends in ashoulder on which the weight of the cover rests.

11K. Morn-SPACE DRAWER UNIT (FIG. 18)

Figs. 18 and 18A show an apparatus unit (block translator BT) whichoccupies more than one drawer space within the frame upright on which itis mounted. As indicated in Fig. 3, the block translator occupies drawerspaces '5 and in control bay BLC of frame BL.

The unit BT includes two end plates I341, secured together by theunderlying longitudinal tie bar I3l, preferably welded to each. Uprightangle bars I32 are secured, as by welding, to the front end of platesI39 to provide a mounting location for L-shaped members I33, detachablysecured thereto as by screws (not shown).

Members I33 are magnetic return members for relay apparatus as disclosedin the noted Bellamy et al. application for Electromagnetic Relays. Thisapparatus includes electromagnets I33 and contact assemblies I45controlled thereby to provide the relay apparatus of the blocktranslator as shown in Fig. 18 of the noted Bellamy and Bowserapplication.

The apparatus at the rear of unit ET includes groups of terminal pinsI31 assembled in blocks to provide the translator terminal pins shown inFig. 19 of the identified Bellamy and Bowser application. The pins I31extend through their mounting blocks as shown in Fig. 18A to permitlocal cable wire (not shown) to be attached ,1

thereto on the inside face of the rear assembly, and to permit localjumper wires (not shown) to be attached to pins I31 on the exposed rearface of the unit.

The blocks in which pins It? are secured are maintained in theirillustrated assembled position by clamp bolts I39, extending betweenlower and upper clamp bars I34 and I35.

The pin-block assembly is secured to end mem bers I35 by hinge pins I35which pass through the down-turned ends of the lower clamp bar I34,thereby enabling the pin-block assembly to be rotated outwardly whenaccess to the local wiring between the relay and pin-block assemblies isdesired. Latch bars I38, detachably secured between the front and rearassemblies as by bolts, normally maintain the illustrated uprightposition of the hinged pin-block assembly.

End plates I30 are each provided with a pair of rollers 51 through whichthe unit ET is mounted in slide mechanisms to operate as a drawer, asdescribed in connection with Figs. 6 to 8. Rollers 51 are so placed onunit B'I that, when mounted to slide within a given drawer space, thelower part of the unit occupies that drawer space, while the upper partof the unit occupies the next overlying drawer space, but makes no useof the drawer-slide mechanism thereof. Such slide mechanism may,therefore, be omitted from the last-noted drawer space.

It is contemplated that, when required, the unit BT may be extendeddownward (as by longer Vertical bars I32) to accommodate dependingequipment which will be accommodated in a third drawer space, the oneimmediately under-- 18 lying the one containing the slide mechanism inwhich the rollers 5! of the unit are received. Such an extendedthree-space. unit will thus be drawer-mounted in the intermediate one ofthe three drawer spaces which it occupies within the switchboard.

IIL. RELAY-DRAWER UNIT (Fro. 19)

Fig. 19 shows relay drawer RD, an apparatus unit for mounting a largeamount of relays, and related equipment within a single drawer space ofthe switchboard. The apparatus on such a unit may be the previouslynoted miscellaneous relay equipment of frame BL (see Fig. 3) or may beany one of the items referred to hereinbefore as a line controller or ablock controller.

structurally, relay drawer RD is composed of similar L-shaped end platesM5 and L-shaped magnet relay bars I45 connecting the end plates andremovably secured thereto, as by screws (not shown) entering theinturned flanges of the end plates. Each end plate It! is provided witha pair of rollers 51 for cooperation with slide mechanisms ashereinbefore described for the crossbar switches.

Relay apparatus (including electromagnets it?) may be mounted on bars itas described for bars I33 of Figs. 13 and 18A.

IIM. Bnccn-Coormn MoUNTiNe (Free 20, 21)

As described, each primary bay GLPI to BLP5 of frame BL, has mountinglocations for two drawer-mounted primary cross-bar switches in itsdrawer spaces 9 and Ill, and has mounting locations in its drawer spacesI to 8 for respectively associated sections of block couple-rs, onesection at the front of the bay and the other at the rear. Each sectionincludes twenty block couplers associated respectively with theverticals of the associated one of the crossbar switches, as disclosedin the noted Bellamy and Bowser application.

Twenty block couplers I50, comprising the section at the rear of thefinal ba BL-P5, are shown in part in Fig. 20 where the concerned doorpanels II5 are broken away. Each coupler I50 is an L-shaped magneticbar, such as parts I33 and I45 of Figs. 18 and 19, together with relayapparatus and counting apparatus mounted thereon as disclosed in the twonoted Bellamy and Arthur applications. Such apparatus wired as shown,for example, in Fig. 5 of the Bellamy and Bowser application. The relayand counter apparatus has not been shown in Figs. 20 and 21 to avoidcrowding the lines on the drawings.

As shown in Fig. 21 for a portion of the lefthand end of bay BL--P5, theblock couplers I50 of any primary bay are supported at each end onsupport angle bars I5I welded to the upright structural members, whichcorrespond to El, 24, and 22, 25 of Fig. 7. The horizontal web of eachsupport bar I5I is notched at points I52 to receive the depending web oftwo block-coupler angle bars I55, one for the front section and one forthe rear section. The end portion of the horizontal web of each bar I50rests on the portion of the horizontal web of its support bar I5! whichextends outwardly from the concerned notch I52,.and the two webs may befastened together, as by screws (not shown) Terminal pins I54 aremounted in blocks supported on bars I55 which lie centrally between thetwo front .and rear couplers I50 on the same level. Pins I54 serve toterminate the switch-

